1. Technical Field
The field is quenching a sheet of hot glass during the scoring process with a jet of water.
2. Technical Background
A fusion process (e.g., downdraw process) forms high quality thin glass sheets that can be used in a variety of devices such as flat panel displays. Glass sheets produced in a fusion process have surfaces with superior flatness and smoothness when compared to glass sheets produced by other methods. The fusion process is described below with respect to FIG. 1 (Prior Art) but for a more detailed description refer to co-assigned U.S. Pat. Nos. 3,338,696 and 3,682,609, which are incorporated herein by reference in their entireties.
FIG. 1 shows a schematic view of an exemplary glass manufacturing system 10 which utilizes the fusion process to make a glass sheet 12. As shown, the exemplary glass manufacturing system includes a melting vessel 14, a fining vessel 16, a mixing vessel 18, a delivery vessel 20, a fusion draw machine (FDM) 22, and a traveling anvil machine (TAM) 24. Typically the components 16, 18 and 20 are made from platinum or platinum-containing metals, but they may also comprise other refractory metals.
The melting vessel 14 is where the glass batch materials are introduced as shown by arrow 26 and melted to form molten glass 28. The melting vessel 14 is connected to the fining vessel 16 by a melting to fining vessel connecting tube 30. The fining vessel 16 has a high temperature processing area that receives the molten glass 28 (not shown at this point) from the melting vessel 14 and in which bubbles are removed from the molten glass 28. The fining vessel 16 is connected to the mixing vessel 18 by a finer to stir chamber connecting tube 32. And, the mixing vessel 18 is connected to the delivery vessel 20 by a stir chamber to bowl connecting tube 34. The delivery vessel 20 delivers the molten glass 28 through a downcorner 36 into the FDM 22 which includes an inlet 38, a forming vessel 40 (e.g., isopipe), and a pull roll assembly 42.
As shown, the molten glass 28 flows from the downcomer 36 into the inlet 38 which leads to the forming vessel 40 which is typically made from a ceramic or a glass-ceramic refractory material. The forming vessel 40 includes an opening 44 that receives the molten glass 28 which flows into a trough 46 and then overflows and runs down two lengthwise sides 48 (only one side shown) before fusing together at what is known as a root 50. The root 50 is where two lengthwise sides 48 come together and where the two overflow walls of molten glass 28 rejoin (e.g., refuse) to form the glass sheet 12 which is then drawn downward by the pull roll assembly 42. The glass sheet cools as it is drawn, transitioning from a molten state at the root, to a visco-elastic state and finally to an elastic state. The pull roll assembly 42 delivers the drawn glass sheet 12 which, at the bottom of the isopipe is substantially flat, but which later in the process may develop a slightly bowed or curved shape across the width and/or length of the glass sheet 12. This bowed shape may remain in the glass sheet 12 all the way to the TAM 24. The TAM 24 has a laser-mechanical scoring device 52 and a nosing device 54 which are used to score the drawn glass sheet so it can then be separated into distinct pieces of glass sheets 56. The TAM 24 is located in the elastic region of the sheet in an area referred to herein as a bottom of the draw 58.
More specifically, FIG. 2 (Prior Art) is a schematic view showing a laser scoring process at the TAM for use on a hot glass sheet 12. The glass sheet has a major surface 60, a first side 62 and a second side 64. Laser scoring and quenching occur from the first side to the second side, or vice versa, across the width of the glass. A laser beam is formed by using a laser 68, such as a stationary CO2 laser mounted to the floor 70, to form a laser beam 72. The laser beam is expanded (not shown) and redirected, for example, using two mirrors 74 into an optical head 76. There the laser beam may then be transformed by one or more lenses 78, such as a pair of cylindrical lenses, to form a laser beam having an elliptical footprint. The laser beam is then redirected using a mirror 82 onto the major surface 60 of the glass. The laser beam having the elliptical footprint is used to heat the glass sheet in a localized area along the desired line of separation or score line 84. The optical head moves across the width of the glass sheet along a linear slide 86 while the TAM 24 travels vertically (along path 88) the same speed as the glass sheet (which is moving along path 90) such that there is no relative motion between the TAM and the glass.
FIG. 2 shows the optical head 76 and a quenching nozzle assembly 92 in front of it, which are movable along the linear slide of the TAM for movement across the width of the glass. This figure shows the devices in an initial position at the first side 62 for laser scoring and quenching and then toward the second side 64, shows the affected areas of the glass resulting from laser scoring and quenching. The glass sheet is first nicked or scored at 96 along one edge of the glass sheet by a mechanical scribe (not shown). This crack initiation point is then used to form a crack 98, by movement of the laser beam across the glass sheet and then quenching with a cooling stream in the path of the desired line of separation. The figure shows the laser beam position after it passes the mechanical nick made in the glass. The laser beam spot 66 travels across the width of the glass sheet to trace the path of the scoreline 84. The beam is moved relative to the glass at a speed on the order of 200 to 1000 millimeters per second. As the laser beam heats the surface of the glass, the nozzle assembly 92 following a close distance behind a tail of the laser spot 66 sprays the glass with a jet of highly cohesive water 100. When performed with the correct thermal balance (taking into account beam profile, beam energy, process speed, water volume and the distance between the water nozzle behind the beam) this rapid cooling of the glass surface generates a tensile stress sufficient to generate a median crack 98 from the preexisting starter defect (crack initiation point) and propagates it across the glass surface toward the second side 64 at process speeds. The crack extends only partway into the thickness of the glass. A conventional robotic apparatus below the TAM (not shown) holds the sheet with suction cups, bends the sheet and breaks it along the score line. The TAM 24 operates in cycles, the cycle beginning at the first side 62 of the glass at a location that is above the location where the glass will be bent and separated. The optical head 76 and quenching nozzle assembly 92 move along the score line from the first end 62 toward the second side 64 of the glass, while the glass and the TAM continue to travel vertically downward at the same rate. The TAM then reaches the end of its stroke at the second side 64 once the laser scoring and quenching processes are completed. The glass bending is carried out along the score line and the robotic equipment located near but below the score line at this point of downward travel of the sheet, separates an individual glass sheet from the ribbon. The TAM moves upward, returning to the beginning of the stroke at the first side 62 of the glass.